US20060180201A1 - Piston-activated valve and methods and apparatus for restraining free play in a device - Google Patents

Abstract

Apparatus and methods for fitting mechanical parts to minimize prevent free play are described. An apparatus having a piston is designed so as to restrain the piston before actuation, and so as to allow the piston to gain momentum before striking an object. The described apparatus are applicable to devices involving shearable elements. An embodiment of the invention relates to a pyrotechnically activated valve incorporating such features to minimize free play in conjunction with such features so as to restrain the piston and also allow the piston to gain momentum.

Description

• This application is a divisional of Applicant's Ser. No. 10/044,934 filed in the U.S. Patent & Trademark Office on 15 Jan. 2001, and assigned to the assignee of the present invention.
CLAIM OF PRIORITY
• This application makes reference to, incorporates the same herein by reference, and claims all benefits accruing under 35 U.S.C. § 119(e) and §120 from my application PISTON-ACTIVATED VALVE filed as a provisional application in the U.S. Patent and Trademark Office as U.S. application Ser. No. 60/261,199, filed on Jan. 16, 2001.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates to mechanical fittings and tolerancing, in particular to fittings found in shearable devices, and more particularly to pyrotechnically activated devices such as valves.
• 2. Background of the Invention
• Pyrotechnic valves are commonly used in rockets for valves which must be opened reliably one time. Typically, these valves contain a seal tube which holds a pressurized gas, and this seal tube is pyrotechnically sheared to open the sealed end of the seal and start the flow of gas. The seal tube typically needs to be very strong in order to support the high gas pressure, such as by helium gas, dictated by the design. Also, initiator redundancy is typically needed to promote reliability. Moreover, for reliability, for example, these devices are typically built with two pyrotechnic initiators for redundancy. Also, the valve typically must be able to function using only one initiator loaded to 75% or with two initiators loaded to 125%. Such valve requirements create a range of initial ballistic gas pressures with a ratio of approximately 4:1, for example. Further, peak pressures are limited by the ability of O-rings and other gas-tight fittings to contain such pressures.
• One potential method of addressing the above described needs in a pyrotechnic valve is to have the piston supply a much larger force at the beginning of a stroke. This could be accomplished, for example, by either increasing the initial ballistic gas pressure or by increasing the area of the piston that is acted on by the gas. However, such pressure increase in this first potential method can be unacceptable because of a need for initiation redundancy in the device.
• A second potential method of addressing the above desired needs in a pyrotechnic valve is to increase the piston area, which can be undesirable for two reasons. First, increasing the piston area can make the piston physically large and heavy. Second, more propellant charge or possibly even an additional booster charge would be required in the initiators. These characteristics can be undesirable from a design standpoint and can generally raise the cost of the pyrotechnic valve device.
• Moreover, the construction of pyrotechnic valve devices must be done to exacting tolerances. Pyrotechnic valve devices, such as those used in rocketry, for example, are often subject to considerable vibration. If there is “play” between the parts, vibrational damage can result.
SUMMARY OF THE INVENTION
• It is therefore an object of the present invention to provide an improved shearable device.
• A yet further object of the invention is to provide an improved shearable device for use with pyrotechnic initiators.
• It is further an object of the invention to provide a device which is less sensitive to vibration.
• A still further object of the invention is to provide an improved pyrovalve.
• These and other objects are met by the present invention. In one embodiment, the present invention provides a method and apparatus for preventing free play in a device, such as a pyrotechnic valve device. An apparatus of this embodiment includes an eccentric sleeve, that is, a sleeve with a cylindrical outer surface and a bore which is not coaxial with the outer surface. Rotation of the eccentric sleeve adjusts the position of the bore in the eccentric sleeve, which is mated with a pin, such as a shear pin.
• In another embodiment of the present invention, the present invention provides a method and apparatus for a device, such as a pyrotechnic valve device, the apparatus of this embodiment including a piston which is driven to strike an object. The piston is mounted to a mount in the device by a shear pin, and upon application of force, the shear pin shears and the piston moves through a gap before striking the object. An apparatus of this embodiment includes: a mount; a piston adjacent to the mount, the piston having a shape defining the movement direction of the piston; and a shear pin having an end partially inserted in a hole in the mount and another end of the shear pin connected to said piston for restraining the piston relative to the mount, a hammer region being formed on an end of the piston located in the direction of motion of the piston, and a strikable part being mounted in the direction of motion of the piston from the hammer region and separated from the hammer region by a gap. The other end of the shear pin is, in one alternative embodiment, connected to the shear pin through a sleeve, such as an eccentric sleeve. In another alternative embodiment, the shear pin is positioned in a spaced relation with respect to the strikable part in the direction of motion of the piston. In a further embodiment, an end of the shear pin is press fit into the mount.
• Embodiments of the invention as a pyrovalve are also described. In such an embodiment, the pyrovalve includes: a housing having a cylindrical bore; a pyrotechnic initiator mounted in an upper portion of the housing; a seal tube mounted in and extending out of the housing, the seal tube having a generally cylindrical configuration and the axis of the seal tube being positioned perpendicular to the axis of the bore of said housing, the seal tube further including a shearable cap on the end of said seal tube inside the housing; and a piston located inside in the bore of the housing so as to define a direction of motion. The piston includes: a flowpath formed perpendicular to the direction of motion defined by the piston; a hollow formed in a side of the piston, further from the pyrotechnic initiator than the flowpath, and shaped to enclose the shearable cap, the hollow being larger in cross-section than the shearable cap so as to define a gap between an overhang of the piston and the shearable cap; and a shear pin connecting the shearable cap to the piston through a sleeve, for restraining play in said piston. Desirably, the sleeve is an eccentric sleeve.
BRIEF DESCRIPTION OF THE DRAWINGS
• A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:
• FIG. 1A is an embodiment of the present invention in the form of a pyrotechnically activated valve, seen in cross-section before activation of the valve;
• FIG. 1B is a view of the pyrotechnically activated valve ofFIG. 1A shown after activation of the valve;
• FIG. 2 is a cross-section of the valve shown inFIG. 1A, prior to activation of the valve, taken across the line labeled A-A′ ofFIG. 1A and ofFIG. 6B;
• FIG. 3A is a cross-sectional view of a device, such as can be used in a valve device, illustrating a general embodiment of the invention incorporating an eccentric sleeve;
• FIG. 3B is a plan view taken from the bottom of the device ofFIG. 3A;
• FIGS. 4A and 4B are a cross-sectional views of a device illustrating another general embodiment of a device of the invention, respectively before and after actuation of the device, such as a valve device;
• FIG. 5 is a close up of a portion to illustrate the shear pin area of the valve device shown inFIG. 1A;
• FIGS. 6A-6F are a series of views of the valve device shown inFIGS. 1A and 1B, withFIG. 6A illustrating an external side view of the valve shown inFIGS. 1A and 1B in sectional view along the section line “1A/1B”, withFIG. 6B illustrating an external front view of the valve ofFIGS. 1A and 1B with the sectional view ofFIG. 2 taken along line A-A′ and with the sectional view ofFIG. 6F taken along the line “6F”, withFIG. 6C illustrating a right side view of the valve ofFIGS. 1A and 1B, withFIG. 6D illustrating a top external view of the valve ofFIGS. 1A and 1B, withFIG. 6E illustrating a bottom external view of the valve ofFIGS. 1A and 1B, and withFIG. 6F illustrating a partial sectional view of the valve ofFIGS. 1A and 1B taken along the sectional line “6F” ofFIG. 6B;
• FIGS. 7A-7C are a series of views of the eccentric sleeve of the valve device shown inFIGS. 1A and 1B, withFIG. 7A illustrating a left side external view of the sleeve ofFIGS. 1A and 1B, withFIG. 7B illustrating a sectional view of the sleeve ofFIG. 7A taken along the section line “7B” ofFIG. 7A, and withFIG. 7C illustrating a right side external view of the sleeve ofFIGS. 1A and 1B; and
• FIGS. 8A-8I are a series of views of the piston of the valve device shown inFIGS. 1A and 1B, withFIG. 8A illustrating a front external view of the piston ofFIGS. 1A and 1B, withFIG. 8B illustrating a right side external view of the piston ofFIGS. 1A and 1B, withFIG. 8C illustrating a left side external view of the piston ofFIGS. 1A and 1B, withFIG. 8D illustrating a cross-sectional view of the piston ofFIGS. 1A and 1B illustrated inFIG. 8C taken along line “8D” ofFIG. 8C, withFIG. 8E illustrating a sectional view of the piston ofFIGS. 1A and 1B illustrated inFIG. 8D taken along line “8E” ofFIG. 8D, withFIG. 8F illustrating a top view of the piston ofFIGS. 1A and 1B, withFIG. 8G illustrating a detail view of an O-ring groove on the piston ofFIGS. 1A and 1B as defined by the view illustrated inFIG. 8C, withFIG. 8H illustrating a sectional view of the piston ofFIGS. 1A and 1B illustrated inFIG. 8D taken along the line “8H” ofFIG. 8D, and withFIG. 81 illustrating a bottom view of the piston ofFIGS. 1A and 1B.
DETAILED DESCRIPTION OF THE INVENTION
• An embodiment of a valve device of the present invention is a pyrovalve, that is, a pyrotechnically activated valve. Pyrovalves can be used, for example, in rockets for valves which are activated only once. For example, a pyrovalve can be a normally closed valve mounted in proximity to a main rocket motor. The valve can be installed in a flow path between a pressurized helium tank and the interior of the main motor, for example. During the first phase of flight, the main motor burns to provide propulsion. During this time, the valve remains in the normally closed position, preventing the flow of helium to the motor. When the main rocket motor burns out, the valve is actuated to provide a helium purge to the motor. This brings the motor rapidly to a zero thrust permitting stage separation shortly thereafter.
• An embodiment of a valve device of the present invention as a pyrovalve is shown inFIGS. 1A, 1B,2,5,6A-6F,7A-7C and8A-8I, withFIG. 1A illustrating the pyrovalve in its normally closed position prior to activation. Referring toFIGS. 1A, 1B,2,5,6A-6F,7A-7C and8A-8I, in this embodiment, the pyrovalve is designed to be connected to a gas source at the right side inFIG. 1A, at “inlet fitting” I. The inlet fitting I leads to sealtube2, which is generally machined from a solid material, such as a precipitation hardened stainless steel, with no outlet, to block the flow of gas through the pyrovalve. At an end ofseal tube2 is ashearable cap30, which is an integral part ofseal tube2, theshearable cap30 being formed of the same material as theseal tube2, such as a precipitation hardened stainless steel.Groove40 inseal tube2 “necks down” theseal tube2, and is generally formed by machining. This necking down allows theshearable cap30 to be mechanically sheared when the pyrovalve is actuated, but to withstand the gas pressure of the gas source, such as a helium gas source, prior to shearing. For example, in an actual embodiment of a pyrovalve, theseal tube2 has been designed to withstand internal gas pressures in excess of 12,000 pounds per square inch, butshearable cap30 shears off at a ballistic pressure in the vicinity of 4,000 pounds per square inch to open the flow path F when required. After actuation, the gas, such as helium, will flow from right to left toward the “Outlet Fitting” O in the pyrovalve.
• Continuing with reference toFIGS. 1A, 1B,2,5,6A-6F,7A-7C and8A-8I, withinhousing1 of the pyrovalve is apiston3 formed of a precipitation hardened stainless steel, for example.Piston3 is also shown in greater detail inFIGS. 8A-8I. Thepiston3 can be cylindrical in shape.Piston3 can be seen inFIGS. 1A and 2 to have anupper flowpath45, which becomes the gas flowpath F after activation of the pyrovalve.Piston3 also haslower portion3awhich has a hollow region surroundingshearable cap30. The hollow region is shaped to provide agap37 aboveshearable cap30, and a portion of thepiston3 betweenflowpath45 and the hollow region forms an overhang or hammerregion35, sinceoverhang35 appears to overhang theshearable cap30 as seen inFIGS. 1A and 2.
• Referring again toFIGS. 1A, 1B,2,5,6A-6F,7A-7C and8A-8I, mounted in the end ofseal tube2, and extending away from theseal tube2, is ashear pin5,shear pin5 being formed of any suitable fracturable material, such as aluminum, for example.Shear pin5 is installed in thebore18aofsleeve18. The outside ofsleeve18 is cylindrical in shape, andsleeve18 has acylindrical bore18awhich is parallel to but not coaxial with the outside of thesleeve18. Thus,sleeve18 has aneccentric bore18a.Sleeve18 is shown in greater detail inFIGS. 7A-7C. The outside ofsleeve18 is mounted in abore3binpiston3. Set screws20 pass through a portion of thepiston3 and contact the outside ofsleeve18. Also, the axis Z1 of theseal tube2 is desirably positioned perpendicular to the axis Z2 of thebore1aof thehousing1, as illustrated inFIG. 1A, for example.
• Shown inFIGS. 1A and 2 are O-rings7, seal19, ball bearing orball member21 and lockplug4. Also shown isFaraday cap15, present before installation to prevent accidental discharge of theinitiators16.
• In order to activate the pyrovalve, a sufficient amount of electric current is applied to one or both ofelectrical initiators16. These pyrotechnic initiators produce hot pressurized gas, which are the products of combustion of the pyrotechnic materials contained within them, in the cavity C overpiston3. Gas within this cavity C is sealed by O-rings7. The pressure, acting over the area of thepiston3, produces a force to drive thepiston3 downward as shown in the figures, such asFIGS. 1A and 1B. The motion of thepiston3 is resisted by theshear pin5, which is held in place byseal tube2, a portion of theshear pin5 being held snugly in theseal tube2, such as by being press fit into theseal tube2. Theshear pin5 is designed to shear across the plane whereshearable cap30 at the left side ofseal tube2 mates withpiston3. In this particular design, the force to shear theshear pin5 is nominally around 1,600 pounds. Theshear pin5 is designed to shear off at a lower force than is necessary for the shearing ofshearable cap30 fromseal tube2. For example, in this particular design, theshearable cap30 requires a shear force of approximately 4,000 pounds to shear.
• When the force produced by the gas is sufficient,shear pin5 shears andpiston3 begins to travel downward in the direction of arrow D ofFIG. 1B. Since theshear pin5 is designed to shear more easily than theshearable cap30, theshear pin5 shears off beforeshearable cap30 at the end of theseal tube2. That is,piston3 begins to move before the flow path F opens. Aftershear pin5 shears, thepiston3 accelerates downward in the direction of arrow D, building up kinetic energy until overhang or hammerregion35 in thepiston3 strikes theshearable cap30, theshearable cap30 being designed to be sheared off from theseal tube2. For example, in the specific example shown, thepiston3 travels approximately ¼ inch before striking theshearable cap30. At this point, the kinetic energy of the movingpiston3 is well in excess of the energy required to shear off the end of theseal tube2.
• During the portion of the stroke in which thepiston3 is shearing off theshearable cap30, thepiston3 will generally temporarily slow down. Piston kinetic energy is partially depleted and used as shear energy. Thepiston3 then accelerates as a result of the expanding ballistic gas still acting on thepiston3. At the end of the piston stroke, askirt50 which is machined into thepiston3 flares out into aconical cavity51 formed by the space between thelock plug4 andhousing1, thelock plug4 andhousing1 being made of precipitation hardened stainless steel, for example. The lock provided by theskirt50, flaring out into theconical cavity51, both holds thepiston3 permanently in the final position P and gently slows thepiston3, minimizing shock. In the final position P, illustrated inFIG. 1B, the final lock is engaged and theskirt50 ofpiston3 is in a flared position over thelock plug4. Also, in the final position P, theshearable cap30 of theseal tube2 and the portion ofshear pin5 in theshearable cap30 are restrained in a portion of thecavity51 ofFIG. 1A at or near position S illustrated inFIG. 1B.
• When actuated, as shown inFIG. 1B,shear pin5 can be seen to be broken intopieces5aand5bas illustrated inFIG. 1B.Piece5bis retained inshearable cap30, which has been sheared fromseal tube2.
• A valve, such as that shown inFIGS. 1A and 1B, is typically required to survive a very high-level shock and random vibration environments, such as during the period of time between launch and the actuation of the valve. These environments can be particularly brutal on internal components that have any “free play”. Such free play can allow impact loads on internal components that rapidly cause damage. The valve of the present invention, such as the valve device ofFIGS. 1A and 1B, incorporates a design to minimize such free play, which is depicted more generally inFIGS. 3A and 3B.
• Referring now toFIGS. 3A and 3B, inFIG. 3A, an embodiment of a device of the present invention, such as can be used in a valve device to minimize free play, is shown havingpart303 andpart310, whereparts303 and310 are connected so as to avoid free play in the directions shown by double headedarrow320.Part303 has acylindrical bore303ain whichsleeve318 is fitted.Sleeve318 has a cylindrical outer surface which fits snugly into thebore303ainpart303.Sleeve318 also has acylindrical bore318awhich is parallel to, but not coaxial with, the outer cylindrical axis ofsleeve318. That is,sleeve318 has aneccentric bore318a.Pin305, such as a shear pin or any shearable feature ofpart310, extends frompart310.Pin305 is cylindrical and fits snugly into the bore ofsleeve318.
• In using the device of the present invention ofFIGS. 3A and 3B,sleeve318 is rotated within thebore303ainpart303. As seen inFIG. 3B, sincesleeve318 is eccentric, rotation ofsleeve318 would cause thebore318ainsleeve318 to rotate around the axis A of thebore303ainpart303, and this allows for negligible variation in the position ofpin305 in the direction ofarrow320, but sufficient variation in the lateral direction L, as indicated by the double-headed arrow L inFIG. 3B, so as to allow the assembly of parts manufactured to reasonably large tolerances.
• The device ofFIGS. 3A and 3B can also include a securing means, such as aset screw330. Afterpin305 is inserted intosleeve318, setscrew330 is tightened to lock and possibly deformsleeve318, thus locking the position ofpin305 with minimal or no free play.
• This general design of a device for minimizing free play, as shown inFIGS. 3A and 3B, is incorporated into the pyrotechnic valve shown inFIGS. 1A and 1B. In the pyrotechnic valve ofFIGS. 1A and 1B, thepiston3 has to be contained due to the vibration of the environment during use. Free play of 0.010 to 0.020 inches, for example, would lead to impact loads which would destroy the shear pin. Thus, in the design of a device for minimizing free play incorporated and shown inFIG. 1A, one end ofshear pin5 is press fit intoshearable cap30 ofseal tube2. Also, thepin305 can be integrally formed as a part ofpart310, as illustrated inFIG. 3A, for example.Sleeve18 is incorporated to slip fit intobore3aofpiston3. The eccentric design ofsleeve18 allows alignment ofshear pin5 intosleeve18 by rotation of thesleeve18, thereby avoiding or minimizing free play in the connection ofshear pin5 topiston3, and thereby reducing any free play to only approximately 0.001 to 0.002 inches, for example. Set screws20, in conjunction with ball bearing orball member21 as the securing means, further lock and deformsleeve18, and further prevent or further minimize any free play.
• The valve shown inFIGS. 1A and 1B also incorporates a design which allows thepiston3 to gather momentum before striking theshearable cap30, as can be used in conjunction with thesleeve318 ofFIGS. 3A and 3B, as described above. This type of design is described more generally with reference to a general embodiment of the present invention as shown inFIGS. 4A and 4B.
• Referring toFIGS. 4A and 4B, inFIG. 4A, a device is shown includingmount410 andpiston403.Mount410 can be a cylinder in whichpiston403 rides, or can more generally be any part providing a guide surface for the downward motion of thepiston403. Likewise,piston403 may be a cylindrical piston, or can be of any of a variety of shapes which can travel downward in the direction of the arrows indicating a propellingforce460 as shown in theFIGS. 4A and 4B.Piston403 is mounted to themount410 byshear pin405, which is inserted into holes orapertures410aand403ainmount410 andpiston403, respectively.
• Continuing with reference toFIGS. 4A and 4B, the lower part ofpiston403 has hammer surface or hammerregion435 which is designed to deliver a blow to strikable part orshearable element430 when thepiston403 moves.Part430 can be any part to be struck. There is agap470 between thehammer surface435 of thepiston403 and theshearable element430.
• In the particular embodiment illustrated inFIGS. 4A and 4B, strikable part orshearable element430 is attached to astationary part440. As illustrated inFIGS. 4A and 4B,stationary part440 is mounted to mount410, butstationary part440 could be mounted to anything stationary relative to thepiston403. Also, as shown inFIG. 4A,piston403 can have aledge445 which is not aligned withhammer surface435.
• In operation, a propellingforce460, indicated by the arrows inFIGS. 4A and 4B, is applied to the top ofpiston403. This propelling force can be gas pressure, pneumatic pressure, an electric or mechanical force, etc. When the force reaches a certain value,shear pin405, which is spaced from theshearable element430 in the direction of travel or motion of thepiston403, as illustrated inFIG. 4A, shears and thepiston403 moves downward in the direction of thearrows460 indicating the propelling force inFIGS. 4A and 4B. Alternatively, when the mount corresponds to a seal tube, such asseal tube2 ofFIGS. 1A and 1B, thepin405 can be press fit into theshearable cap30 of theseal tube2, as described previously with respect toFIGS. 1A and 1B.Piston403 moves throughgap470 before hitting the strikable part ofshearable element430. Thuspiston403 is able to gather momentum before impact with the strikable part orshearable element430. When used as a valve device, such as illustrated inFIGS. 1A and 1B, the shearing of theshearable element430 would typically create a flow path G formed integrally as a passage in thepiston403, the location of the flow path G being indicated inFIG. 4B.
• In the particular embodiment shown inFIGS. 4A and 4B, the strikable part orshearable element430 is sheared offstationary part440 upon impact at ashearable link430aconnecting the strikable part orshearable element430 and thestationary part440. Due to theledge445, thestationary part440 is not hit by thepiston403 whenshearable element430 is impacted by thepiston403.Stationary part440 can thus serve as a detent for stopping the downward motion of thepiston403. In such a case, the total stroke of thepiston403 is given bygap450 illustrated inFIG. 4A. In general, there will be some sort of a detent for stopping the piston after it has hit the object to be worked on.
• Although shown inFIGS. 4A and 4B for a shearable object, the device of the present invention illustrated inFIGS. 4A and 4B is applicable to any object to be struck. For example, hammer surface or hammerregion435 could be striking a rivet or nail, punching a hole, making an impression, etc., for example.
• In the pyrovalve embodiment shown inFIGS. 1A and 1B, however,piston3 is mounted by means ofshear pin5 toshearable cap30 which is part ofseal tube2, which is held in place by thehousing1, and theshear pin5 is not initially spaced from theshearable cap30 in the direction of travel or motion of thepiston3. Upon activation, thepiston3 moves downward, andoverhang35 moves throughgap37 before strikingshearable cap30. In the invention as shown inFIGS. 1A and 1B, the interaction ofskirt50 with the conical cavity formed by the space between thelock plug4 andhousing1 serves as the detent.
• In the pyrovalve of the invention, the piston design, incorporating the sleeve design to minimize free play, allows the piston to gain momentum before striking the shearable cap. One result of this design is that less of the pyrotechnic explosive is required to shear the cap than in a comparable design with no shear pin in which the piston initially contacts the shearable cap.
• While there have been illustrated and described what are considered to be preferred embodiments of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made, and equivalents may be substituted for elements thereof, without departing from the true scope of the present invention. In addition, many modifications may be made to adapt a particular situation to the teaching of the present invention without departing from the scope thereof. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the present invention, but that the present invention include all embodiments falling within the scope of the appended claims.

Claims (26)

1. An apparatus, comprising:

a first part including a bore;

an eccentric sleeve mounted in said bore of said first part, said eccentric sleeve including outer surface corresponding to the bore of said first part, and said eccentric sleeve including a bore which is parallel to and not coaxial with the outer surface of the eccentric sleeve; and

a second part comprising a pin corresponding to the bore in said eccentric sleeve, said pin for insertion in the bore in said eccentric sleeve.

2. The apparatus ofclaim 1, further comprising:

a scuring means passing through said first part, the securing means for contacting the outer surface of said eccentric sleeve.

3. The apparatus ofclaim 2, further comprised of said securing means comprising a set screw passing through said first part.

4. The apparatus ofclaim 2, further comprised of said securing means comprising:

a ball member for contacting the outer surface of said eccentric sleeve; and

a set screw passing through said first part, with an end of said set screw contacting said ball member.

5. The apparatus is claimed inclaim 2, further comprised of said first part comprising a piston, and said second part further comprising a seal tube, with an end of said pin for insertion in said seal tube.

6. The apparatus ofclaim 1, further comprised of said first part comprising a piston, and said second part further comprising a seal tube, with an end of said pin for insertion in said seal tube.

7. An apparatus, comprising:

a first part including a bore;

a sleeve mounted in said bore of said first part, said sleeve including an outer surface corresponding to the bore of said first part, and said sleeve including a bore; and

a second part comprising a pin corresponding to the bore in said sleeve, said pin for insertion in the bore in said sleeve.

8. The apparatus ofclaim 7, further comprising:

a securing means passing through said first part, said securing means for contacting the outer surface of said sleeve.

9. The apparatus ofclaim 8, further comprised of said securing means comprising a set screw passing through said first part.

10. The apparatus ofclaim 8, further comprised of said securing means comprising:

a ball member for contacting the outer surface of said sleeve; and

a set screw passing through said first part, with an end of said set screw contacting said ball member.

11. The apparatus ofclaim 8, further comprised of said first part comprising a piston, and said second part further comprising a seal tube, with an end of said pin for insertion in said seal tube.

12. The apparatus ofclaim 7, further comprised of said first part comprising a piston, and said second part further comprising a seal tube, with an end of said pin for insertion in said seal tube.

13-29. (canceled)

30. A pyrovalve, comprising:

a housing including a bore;

a pyrotechnic initiator mounted in an upper portion of said housing;

a seal tube mounted in and extending out from said housing, with an axis of the seal tube being positioned perpendicular to an axis of the bore of said housing, said seal tube further comprising a shearable cap on an end of said seal tube located inside the housing;

a piston located inside in the bore of said housing so as to define a direction of motion for the piston, said piston comprising:

a hollow formed in a side of the piston, said hollow for receiving said shearable cap, said hollow being larger in cross-section than the shearable cap so as to define a gap between an overhang of the piston and said shearable cap; and

a shear pin connecting said shearable cap to said piston through a sleeve, for restraining play in said piston.

31. The pyrovalve ofclaim 30, further comprising:

a first portion of said shear pin for insertion into an aperture in said shearable cap;

said piston including a bore for surrounding said sleeve including a second portion of the shear pin not located in said aperture of the shearable cap;

said sleeve for insertion into the bore of said piston, said sleeve including an outer surface corresponding to said bore of said piston, and said sleeve including a bore corresponding to the second portion of the shear pin and oriented parallel to and not coaxial with the outer surface of the sleeve; and

said second portion of said shear pin for insertion into said bore of said sleeve.

32. A pyrovalve, comprising:

a housing including a bore;

a pyrotechnic initiator mounted in an upper portion of said housing;

a seal tube mounted in and extending out from said housing, with an axis of the seal tube being positioned perpendicular to an axis of the bore of said housing, said seal tube further comprising a shearable cap on an end of said seal tube located inside the housing;

a piston located inside in the bore of said housing so as to define a direction of motion for the piston, said piston comprising:

a hollow formed in a side of the piston, said hollow for receiving said shearable cap, said hollow being larger in cross-section than the shearable cap so as to define a gap between an overhang of the piston and said shearable cap; and

a shear pin press fit in an aperture of said shearable cap and for being coupled to said piston, for restraining play in said piston.

33. The pyrovalve ofclaim 32, further comprising:

a first portion of said shear pin for insertion into an aperture in said shearable cap;

said piston including a bore for surrounding a second portion of the shear pin not located in said aperture of the shearable cap;

a sleeve for insertion into the bore of said piston, said sleeve including an outer surface corresponding to said bore of said piston, and said sleeve including a bore corresponding to the second portion of the shear pin and oriented parallel to and not coaxial with the outer surface of the sleeve; and

said second portion of said shear pin for insertion into said bore of said sleeve.

34. The pyrovalve ofclaim 32, further comprising:

a first portion of said shear pin for insertion into an aperture in said shearable cap;

said piston including a bore for surrounding a second portion of the shear pin not located in said aperture of the shearable cap;

a sleeve for insertion into the bore of said piston, and said sleeve including a bore corresponding to the second portion of the shear pin; and

said second portion of said shear pin for insertion into said bore of said sleeve.

35. A method for restraining free play in an apparatus, comprising the steps of:

providing a first part including a bore;

mounting a sleeve in said bore of said first part, said sleeve including an outer surface corresponding to said bore of said first part, and said sleeve including a bore;

inserting a pin into the bore in said sleeve.

36. The method ofclaim 35, further comprising the steps of:

passing a securing means through said first part; and

contacting an outer surface of said sleeve by said securing means to restrain free play in said first part.

37. The method ofclaim 37, further comprising the steps of:

providing a second part; and

inserting an end of said pin into said second part, to restrain free play in said first part.

38. The method ofclaim 35, further comprising the steps of:

providing a second part; and

inserting an end of said pin into said second part, to restrain free play in said first part.

39. The method ofclaim 38, further comprising the step of:

press fitting into a bore of said second part an end of said pin, and a coupling said second part to said first part through said pin.

40. The method ofclaim 35, further comprised said bore of said sleeve being parallel to and not coaxial with the outer surface of said sleeve.

41. A method for restraining free play, comprising the steps of:

providing a first part including a bore;

providing a second part including a bore;

press fitting a pin into said bore of said second part; and

coupling said first part to said second part through said pin.

42-50. (canceled)

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